When hydrocarbons are trapped in the cracks and pores of a rock, a method for exploiting the corresponding deposit consists of drilling various wells. Some of these wells are then injected with water or another fluid. This liquid penetrates into the fissures and into the rock matrix and thus pushes back the hydrocarbons towards the remaining wells which are used to recover the petrol.
A test is first conducted on each injection well. This test is primarily designed to ascertain the injectivity of the well and to disclose any possible networks of formation fracturings or natural drains likely to short-circuit the flow routes concerning all the fissures and thus resulting in flooding productive wells.
During a conventional test, a predetermines volume of water is introduced from the surface with a constant or linear flow or by means of gaps. During this time, various measurements are made in the well at each perforation level of a tubing inserted therein. Hydraulic measurements are taken and recorded, such as the pressure and temperature of the injected fluid and the flow at the bottom.
So as to better evaluate the hydraulic characteristics of the subsoil, it is preferable and more effective to record other quantities, known as microseismic quantities. However, up until now, these B5 geothermal energy. These microseismic quantities are representative of the acoustic emission of the terrain when, due to the injection of a fluid, the fissures of the rock open and the terrain changes.
For example, the patent application GB 2 230 091 filed in 1989 by the British Secretariat of State for Energy concerns a probe developed with this aim in mind. It is mainly composed of a measurement cartridge comprising accelerometer type sensors, as well as a control cartridge containing hydraulic, electronic systems, etc., and connected to the measurement cartridge by a flexible cable. One or several hydrophones are also preferably added to the two preceding cartridges so as to form a tool combination (i.e., a combination or series of "tools") suitably adapted for being lowered inside a drilling halo.
Apart from other factors, this probe accomodates the amplitude of seismic waves arriving as far as the drilling at each moment and at several locations. The analysis of these measurements gives an accurate indication at the same location where they are made. In the case of an injection well, it can be readily understood that this knowledge allied to that of the evolution of the hydraulic quantities recorded conventionally would give a clearer picture or the flows developing inside the deposit. The technical problem then posed is how to make available a probe able to simultaneously record the hydraulic and microseismic quantities in an injection well.